1. Field of the Invention
The present invention relates to a control system and method of a two cycle direct fuel injection engine and more particularly to an engine control system and method capable of eliminating misfires and improving combustion by means of suspending fuel injection and ignition periodically.
2. Prior Art
In conventional port scavenging two cycle engines, generally the amount of residual gas versus the amount of fresh air increases in the light loading condition and consequently misfires tend to occur cyclically in the cylinder. As a result of this, excessive emissions of unburned hydrocarbons contributing to poor fuel economy are produced.
Miscellaneous techniques to solve these problems have been proposed. Among them, the stratified charge combustion techniques in which fuel is directly injected into cylinders and burned in the stratified manner are effective to prevent misfiring. The conditions to realize the stratified charge combustion are not simple, namely conditions such as the shape of the combustion chamber, the state of fuel spray, the state of gas flow, miscellaneous control values and the like are needed to put into good trim. However, it is generally difficult to realize homogeneous combustion in the high speed and high load conditions with these conditions retained. Especially in the case of small engines with a high specific power, these conditions to realize the stratified charge combustion are difficult to be satisfied.
Therefore, in order to prevent misfires under light load conditions, other techniques than the stratified charge combustion must be chosen. Thus, it is considered to reduce combustion cycles, namely to suspend combustions selectively in the light load condition where misfires tend to occur. By selectively suspending combustions, it is possible to assure a good scavenging in a cycle wherein combustion is suspended and to assure a good combustion in a cycle wherein combustion is undertaken.
As techniques of suspending combustions, for example, Japanese Patent Application Toku-Kai-Sho 62-157259 discloses a technique of selectively suspending fuel injections for a diesel engine and Japanese Patent Application Toku-Kai-Sho 59-65526 also discloses a technique of selectively suspending fuel injections for a port injection type four-cycle engine.
However, in a two cycle direct fuel injection engine, no specific technique of selectively suspending fuel injection has ever been disclosed. Therefore, it is now expected that a two cycle direct fuel injection engine capable of smoothly controlling combustions in light load conditions will be developed.